There are a lot of ways to find commercial property availabilities, I can probably find something for you in your town from my desktop. But are you up to handling this? It would be so much better if you engaged a commercial broker.
Having said that, here's what you do. You contact your state and city government offices and find out if there are incentives being offered for certain types of nonprofits.

Debbie,

Usually depending on square footage, there are spaces both in office buildings and warehouse situations that are not as "desirable".  These usually can be leased inexpensively.  Having said this, I have no idea what your Austin commercial market is like, and like Joe Pryor I would refer it to a commercial agent who has a ton of space listed and may have that remnant space.  A  

Doesn't sound like this is in your wheelhouse so I would find an expert to refer it to.

Have you ever worked with commercial before?

There is no difference finding a commercial property than there is a residential - search your MLS.

By the questions you're asking you may want to consider working with a commercial agent until you get the hang of it.

Debbie Thomas A non-profit organization is handled like any other commercial client. Read over Article 11 of the NAR COE and work accordingly.

I am not aware of any specific place that houses these type of listing resources. I suggest looking for properties that have been on the shelf a long time. These are the type of owners that may want to have a little something and get a writeoff versus holding out much longer for something that may never happen.

If you are active in your regional builders association, you should be in contact with the right people.

Joe Pryor is right.... there is no "fast track" course for that process....

Candice A. Donofrio has an excellent idea!

Debbie Thomas you can find some commercial properties listing at www.loopnet.com/

You have many answers here.

   Talk to commercial brokers in your area, tell them what you are trying to achieve.

I wold start by talking to people I know and agents in the industry

Good luck.

Look for a commercial agent and refer your client to him/her.  Good luck.

"When you start walking the way, the way appears."

Beacon Street needed a home for their teaching, feeding and pantry operations. We made a video and posted blogs.

Each involved group leveraged their vertical and horizontal connections. Even those employed by the cities involved were pressed to share the message.

As you can imagine, many live with hostile emotions regarding what is needed to feed the homeless. Fortunately, in my area, many more still value the call to ease the suffering of the least among us.

The Angel Donor found us. I made sure we could be found. (a real estate agent reality)

Beacon Streets light shines on.

Property is found by digging and scratching. That is the nature of commercial.

Getting the 'deal' accepted relies on the aligned resources. Many commercial properties state 'No Non-profits (specifically churches) allowed.

MONEY changes the outcome.

The Angel came via vertical connections and committed on a deal that initially fell through. We all hung together until a better site was found.

I wish I know.

Great answers are here. 

I am sure you found the answer here.

Unfortunately I only work residential, but would recommend contacting someone in Commercial in your area.

Out here the local malls have a lot of empty space.  They donated space for an animal rescue storefront.  Maybe some commercial buildings are in a similar state and would rather have cheaper rents than no renters.

I don't know.

Pass the word to all the local commercial brokers and agents.

And have the benefactors of the non profit dig a bit deeper.

Honestly I suggest a referral to a commercial agent.  To best serve the client is our purpose and if commercial isn't your thing... you should refer.